1. Field of the Invention
The present invention is directed to guidance systems, and more particularly to an improvement in a guidance system in which at least one mobile vehicle is guided along a traffic path defined by radiated signals to arrive at a predetermined location along a traffic layout.
2. Description of the Prior Art
Arrangements in which a traffic path has been used in the guidance of a driverless mobile unit along a desired course have been set forth in U.S. Pat. Nos. 3,009,525, and 3,147,817, issued to Robert DeLiban. In such disclosures, the traffic path is defined by a conductor energized to radiate an electro-magnetic field, and a sensing means on the vehicle is operative to detect the radiated energy and to control the vehicle steering means to follow such path.
In the system disclosed in the DeLiban U.S. Pat. No. 3,147,817, a plurality of driverless vehicles equipped with sensing means are operative to simultaneously follow energized conductor paths in a safe and reliable manner. In the patented arrangement, station selection means provided on each vehicle instruct the vehicle to proceed to any one of a plurality of stations located at different points along the path. Location-identification means at each station provides a unique code signal which is detectable by code sensing means on the vehicle, as the vehicle approaches a station, to enable halting of the vehicle when the vehicle arrives at the station selected.
The system includes a main traffic path and a plurality of secondary paths which branch away from the main path at different points designated as decision points, and whenever the vehicle arrives at a decision point in the system, one of at least two alternate paths is selected as a preferred path to a selected station. Each decision point includes an associated location-identification means which provides a unique code for the decision point. The code sensing means on the vehicle detects such code as the vehicle approaches the decision point, and a comparison means automatically controls the vehicle to follow the one of the paths which is predetermined as the preferred path from the decision point to the selected station.
The system further includes a beacon signalling arrangement wherein "hold beacons" are disposed along the layout of the guidance system, whereby each vehicle senses the presence of another vehicle preceding it by less than a preassigned minimum distance, and is halted while such other vehicle remains within the minimum distance. The halted vehicle simultaneously signals its presence to any vehicle which may attempt to follow too closely behind.
In this arrangement, each vehicle signals its presence as it passes through a block by radiating a presence signal which is transmitted over conductors to the hold beacon associated with that block. The presence of a vehicle within the limits of the block produces a hold signal at its associated block beacon. As a further vehicle enters the block and draws abreast of the hold beacon, receipt of the hold signal from the beacon is effective to disable the propulsion means of the second vehicle and thus stop the vehicle until the first vehicle leaves the block.
At converging points, a vehicle transmits a hold signal from one block to two separate hold beacons, each of which is positioned adjacent to a different traffic path. The hold signals provided by such beacons are effective to control movements of vehicles at converging points where vehicles traveling over different paths enter a common path.
In the U.S. Pat. No. 3,544,788 to Nicholas J. Guzik there is disclosed an electronic position indication system wherein position information signals are transmitted between trains traveling along the same track. Each train unit includes three position counters to indicate the position of its own train and the positions of train units immediately ahead and immediately behind. Magnetic inducers spaced at predetermined intervals along the track activate an "own train" counter and a radio transmitter in each train to generate a time signal for reception and activation of counters in the immediately ahead and behind train units. Whenever a minimum safe distance between two trains is reached, as indicated by the count difference for the counters, braking is applied to at least the following train.
While this system is effective in maintaining a predetermined minimum spacing between train units travelling over the same track, the system relies on successive pulse counting for indicating the position of each train unit, and the relative spacings between train units.
Another vehicle control system which employs two way communication is disclosed in the U.S. Pat. No. 3,734,229 issued to D. T. Comer. In this system, the traffic layout is defined by an array of conductors disposed along the traffic layout and energized with a low frequency AC signal for developing magnetic fields which are detectable by a vehicle carried guidance control unit.
An array of twin lead conductors disposed beneath the surface of the travel paths form a distributed antenna network provided a communication medium for two way communication between a stationary control unit and vehicle carried control units, permitting transmission of heading command signals to the vehicle from the stationary control unit.